The present invention relates to a gun cartridge, more particularly, a series of and method of making efficient, high velocity gun cartridges for a 50 caliber gun.
The 50 caliber Browning Machine Gun (BMG) was developed in 1917 from John Browning""s design. Its intended use was as an anti-aircraft battery and anti-tank weapon. It was not intended to be used as an anti-personnel weapon. It remains the largest and most heavily used machine gun today.
The original loading was an 800 grain bullet at 2650 feet per second velocity (fps) out of a 46xe2x80x3 barrel. It was later loaded with a 900 grain bullet at 2500 fps. Currently the 50 BMG is loaded with a 650 grain bullet at 3000 fps. The bullets may be AP (armor piercing), API (armor piercing incendiary), APT (armor piercing tracer), ball (steel-cored) or FMJT (full metal jacket tracer). It is designed to be effective past 2000 meters or 2500 yards.
The 50 BMG is no longer used as an anti-aircraft battery. Today it is used for defense on armored personnel carriers, the Bradley fighting machine, and stationary mounted to provide cover for troops. Its long-range capability at 2000+ yards makes it valuable for extreme long-range sniping use when chambered in bolt-action rifles designed around the cartridge. These bolt-action rifles require a special custom-built action to accommodate the large 50 BMG cartridge.
The 50 BMG began to gain popularity among civilians as a 1000 yard target rifle. To feed the public""s interest in the cartridge gun makers developed more sophisticated and more accurate target rifles around this cartridge. Many gun manufacturers began putting on the market their own designs for 50 caliber target rifles, most of which were single-shot. As the popularity of the 50 caliber grew among civilians, the military became interested in it as a long-range sniper cartridge. Now almost all 1000 yard match records are held by the 50 caliber.
Law enforcement and the military have found that when the 50 BMG is adapted to shoulder-held weapons it is far superior to any other shoulder-held weapon in use today. Its large projectile (650 and 750 grain FMJ, of which the 650 grain is most popular) at high velocity translates into awesome power for the shooter.
The 50 BMG suffers from a number of disadvantages including extremely large muzzle flash, very loud report, short barrel life due to throat erosion, and extremely large rifles necessary to accommodate the cartridge. As a machine gun (M2 Browning) the 50 caliber weighs 150+ pounds, and requires 2 to 3 men to set it up. When chambered in a bolt-action sniping type weapon its disadvantages sometimes outweigh its advantages. Also tremendous muzzle flash is a problem. When shooting in the evening or at night the muzzle flash can be easily seen for more than three miles. When shooting low to the ground or from a prone position it kicks up large clouds of dust. This is mainly due to the huge case capacity (overbore) and to the shortening of the barrel, which was necessary to adapt the cartridge to a sniping style rifle. With the shortened barrel a large drop in muzzle velocity occurred. Velocity drops an average of 300 fps.
The 50 caliber has always been valued by the military as an effective and hard-hitting cartridge. It has been used as a platoon support weapon but not as a squad support weapon because of its weight and bulk. Even in a sniping rifle design it is still too cumbersome to carry in many cases.
A significant problem most civilians have with the 50 caliber target rifle is its expense as the guns range from $4000 to $10,000. The ammunition is very expensive, and the components with which to reload for such a rifle are very expensive. The loading press is a special press that is much larger than a standard loading press and about 4 times the cost. The loading dies are larger diameter dies, almost twice the size of standard loading dies, and 10 times the price. Primers for the 50 caliber BMG are a unique design and only fit the 50 BMG. These primers vary from 0.50 to $1 each, depending upon the source.
Also the 50 BMG is what is classified as an inefficient cartridge. Inefficient cartridges, whether they be sporting or military design, burn a more than average amount of powder to gain a small increase in velocity and ft-lbs. of muzzle energy. To illustrate inefficiency in more understandable terms, a helpful example is a trawler that can be moved across water at 9 knots using two 120 horsepower engines. To increase the speed at which the trawler moves across the water to 10 knots would require two 200 horsepower engines. This is a vast increase in power and fuel consumption for a one knot gain in speed. Although the 50 BMG cartridge was designed to be fired in a Browning machine gun with a 46xe2x80x3 barrel, even with that lengthy barrel a great deal of powder remains unburned. This unburned powder is due to the fact that there was much more powder in the case than the bore can consume efficiently, which was also the reason for the large muzzle flash.
Another 50 caliber cartridge is the 500 Whisper. The 500 Whisper was built on the shortened 460 Weatherby case, the same as the alternate embodiment of the present invention. The difference between the two is that the 500 Whisper was built on a shortened 460 Weatherby case, 2.5xe2x80x3 overall case length. This cartridge was intended as a subsonic round. Subsonic means velocities at 1100 fps or slower. The cartridge uses a 750 grain bullet and was intended for long-range sniping use with no sound. The 500 Whisper was built on a 24xe2x80x3 barrel rifle.
The 500 Whisper suffers from too small of a case capacity which results in an inefficient cartridge. The small capacity is a result of the 500 Whisper being designed to be subsonic thus it is only useful as a subsonic sniping round. It is not useful for a squad, infantry or attack rifle. Additionally, the Whisper 500 was designed for firing in an urban setting so the marksman could remain undetected and still penetrate a kevlar helmet at 600 yards. The gun cartridges of the present invention are more versatile and capable of much higher velocity and penetration of a kevlar helmet at much greater ranges (in excess of 2000 yards).
Yet another 50 caliber cartridge is the 50 Caliber Spotter Round. This was built on a shortened 50 caliber BMG case. The case had an overall length of 2xe2x80x3. It was intended as a spotter round in tank artillery and occasionally used in machine guns in aircraft. It came into use during WWII and has not been used since. This cartridge uses a shortened 50 BMG case but the rim size of 0.804 inches is too large to fit any shoulder held weapons. Moreover, it will only fit guns already fitted for the 50 BMG.
There are a number of terms associated with guns, bullets and cartridges that are defined and used herein as follows:
Barrel Life (Throat Erosion): The condition of overheating and eroding the throat area (the part of the chamber where the bullet contacts the rifling) of a rifle barrel by large amounts of slow burning powder down a relatively small bore.
Cannelure: Circumferential groove(s) around a bullet or cartridge case. Used for identification, to hold lubricant, or to crimp case into.
Capacity: Volume; ability to contain a substance
Disintegrating bullet: A bullet made of a carbon powder pressed together under high pressure so the bullet fragments are turned back to powder when hitting extremely hard substances, such as steel or concrete walls.
Efficient: Marked by an ability to use the most effective and least wasteful means of accomplishing a purpose or doing a task.
Efficiency: Performance of a task with little or no wasted effort; capability to produce desired results with a minimum expenditure of energy.
Force Multiplier: A means of increasing the firepower of an individual, a squad (a seven to twelve man team), a platoon (four to five squads), or a company (four to five platoons) without adding additional personnel or equipment.
Inefficient: Wasteful of energy in performing a task; or underpowered and therefor incapable of performing a task to optimal standards.
Overbore Capacity: Any cartridge that has a volume too large in relation to bore diameter with normally available powders.
Sniper: One that fires at exposed men or equipment of an enemy at a long distance.
The cartridges of the present invention can be made on much shorter barrels with much less or virtually no muzzle flash, and shorter actions, which translates into a much more easily controlled weapon, and one that can be carried and shouldered by an individual. Thus, the cartridges of the present invention allow rifles to be designed that are much less cumbersome than the 50 BMG, and still allow second and third shot capability without losing the point of aim.
The present invention provides a method of determining the efficiency of a gun cartridge by determining the water weight volume of the cartridge; determining the bore diameter of the gun barrel; determining the weight of the bullet; and calculating the efficiency rating of the cartridge by multiplying the water weight volume by the bore diameter and dividing by the bullet weight. The efficiency rating is optimal between 110 and 145 when the water weight volume is determined in grains, the bore diameter is determined in thousandths of inches and the bullet weight is determined in grains. There are 7000 grains in one pound. One such 50 caliber gun cartridge has a casing diameter of approximately 0.688 inches and neck portion which accepts a bullet having a bore diameter of approximately 0.510 inches. The case has a preferred length ranging from 1.75 inches to 2.4 inches measured from the primer to the mouth of the neck.